Note: Transliterated title "Plutoniia". Written in 1915, first Russian edition 1924, first English translation 1955.

Synopsis: Publisher's description (2001): "Originally published in 1924, Plutonia is a hollow-earth-type science fiction novel set in an underground world of rivers, lakes, volcanoes, and strange vegetation, a world which has its own sun - Pluto - and is inhabited by monstrous animals and primitive people. The author uses the plot for the purpose of introducing the reader to the animal and plant life of ancient geological periods in their natural surroundings."